An agricultural seeding machine such as a row crop planter or grain drill places seeds at a desired depth within a plurality of parallel seed trenches formed in soil. In the case of a row crop planter, a plurality of row crop units are typically ground driven using wheels, shafts, sprockets, transfer cases, chains and the like. Each row crop unit has a frame which is moveably coupled with a tool bar. The frame may carry a main seed hopper, herbicide hopper and insecticide hopper. If a granular herbicide and insecticide are used, the metering mechanisms associated with dispensing the granular product into the seed trench are relatively simple. On the other hand, the mechanisms necessary to properly meter the seeds, dispense the seeds at a predetermined rate and place the seeds at predetermined relative locations within the seed trench are relatively complicated.
The mechanisms associated with metering and placing the seeds generally can be divided into a seed metering system and a seed placement system which are in communication with each other. The seed metering system, also referred to herein as a seed meter, receives the seeds in a bulk manner from the seed hopper carried by the frame. Different types of seed meters may be used such as seed plates, finger plates, and seed discs. In the case of a seed disc metering system, a seed disc is formed with a plurality of seed cells spaced about the periphery thereof. Seeds are moved into the seed cells, with one or more seeds in each seed cell depending upon the size and configuration of the seed cell. A vacuum or positive pressure air may be used in conjunction with the seed disc to assist in movement of the seeds into the seed cells. The seeds are singulated and discharged at a predetermined rate to the seed placement system.
The seed placement system may be categorized as a gravity drop system or a power drop system. A seed placement system of the power drop variety generally can be classified as a seed conveyor belt drop, rotary valve drop, chain drop or air drop. Such power drop systems are known and thus not described further.
In the case of a gravity drop system, a seed tube has an inlet end which is positioned below the seed metering system. The singulated seeds from the seed metering system merely drop into the seed tube and fall via gravitational force from a discharge end thereof into the seed trench. The seed tube may be curved in a rearward manner to assist in directing seed into the seed trench. The rearward curvature also assists in reducing bouncing of the seeds back and forth within the tube as it falls therethrough into the seed trench. Further, the rearward curvature reduces bouncing of the seed as it strikes the bottom of the seed trench.
To ensure that the planting unit is operating correctly, the seed tube may be provided with a seed sensor. A light is projected from a light source across the hollow interior of the seed tube to a light receiver located in an aperture of the front wall. When a seed passes between the light source and the light receiver, the seed interrupts the light beam and the seed is detected.
The light source and light receiver are designed to extend into the apertures and be substantially even with the interior surfaces of the front and rear walls. However, sometimes the sensor may extend past the interior surface of the front wall. In this situation, the seed may impact the top edge of the sensor, possibly damaging the seed and deflecting the seed trajectory into the seed trench.
What is needed in the art is a seed tube with a sensor which operates effectively, yet does not interfere with seed drop through the seed tube.